Phosphonic acid-modified microgel dispersion

ABSTRACT

Emulgator-free microgel, dispersed in an aqueous phase, obtainable by producing a polyacrylate (A) in the presence of at least one compound (B) containing a phosphonic acid group, where the polyacrylate (A) has at least one hydroxyl group and at least one carboxyl group; aqueous phase crosslinking of the reaction mixture originating from step a) with an aminoplast resin (C); subsequent emulsion polymerization of the reaction mixture originating from step b) with at least one monomer compound (D) which contains at least one radically polymerizable double bond.

The present invention relates to a microgel and its use in a multilayercoating, in particular in the production painting of automobile bodies.

A multilayer coating totaling four different layers (four-stage system)is generally used for the production painting of automobile bodies;these four layers are applied in succession at separate paint stations:

The first layer located directly on the vehicle sheet metal is anelectrophoretically applied layer (electrocoat, cathodic dip coatinglayer) which is applied by electro dip coating—mainly cathodic dipcoating—for corrosion protection and subsequently baked.

The second layer, on top of the electro coat, is a primer-surfacer about30 to 40 μm thick which on the one hand offers protection againstmechanical attack (stone chip protection) and on the other hand ensuresadequate topcoat holdout, i.e. it smoothes the rough surface of the bodyfor the following topcoat and fills minor irregularities. The paintsused to produce this primer-surfacer coat contain pigments as well asbinders. The wettability of the pigments used has an effect on thetopcoat holdout of the entire multilayer coating and on the gloss of theprimer-surfacer, as demanded by some automobile manufacturers.Application of the primer-surfacer coat is generally carried out throughapplication with electrostatic high-speed rotary bells and subsequentbaking at temperatures above 130° C.

The third layer, on top of the primer-surfacer, is the basecoat, whichgives the desired color to the body through the corresponding pigments.The basecoat is applied in a conventional spraying method. The filmthickness of this traditional basecoat is between about 12 and 25 μm,depending on the hue. This coat, particularly with metallic effectpaints, is mostly applied in two steps. In a first step the paint isapplied by means of electrostatic high-speed rotary bells, followed by asecond application by means of pneumatic atomization. This coat (whenusing water-based basecoat) is interim dried using infra-red heatersand/or warm air convection.

The fourth and topmost layer, on top of the basecoat, is the clearcoat,which is usually deposited in one application by electrostatichigh-speed rotary bells. It gives the body the desired gloss andprotects the basecoat from the effects of the environment (UV radiation,salt water, etc.).

Finally, the basecoat and the clearcoat are baked together.

Additional basic requirements besides its color-imparting properties areplaced on a waterborne basecoat which can be used in this multilayercoating, or in a basecoat produced from it:

For one, the basecoat in its cured state must result in an optimalorientation of the aluminum flakes used as effect pigments. Thisproperty, known by the term “flop effect”, is of crucial importance forany metallic finish. A particularly good “flop effect” is achieved whenthe tiny platelet-shaped effect pigments are aligned as evenly aspossible at a shallow angle to the paint layer.

In addition, the basecoat layer must have a precisely specified adhesionto the paint layers below and above it. The basecoat decisively affectsthe stone chip resistance of the originating multilayer coating ofproduction automobile bodies. It should be noted in this connection thatstone chip resistance is known as a “k.o. criterion,” i.e. only thosemultilayer coatings which have previously passed the VDA stone chip testcan be used in production operations. The final multilayer coatingpasses the test if, under a precisely defined mechanical load, itexhibits pitting which does not exceed a certain area and isattributable to a separation of the basecoat from the primer-surfacercoat underneath it. Consequently, the adhesion of the basecoat must beadjusted in such a way that it is high enough so that the clearcoat doesnot separate from it, but is low enough not to pull the primer-surfacerwith it when chipped by a stone, which would otherwise result inconsiderable corrosion damage to the automobile body.

Secondly, the basecoat must have good workability. This means that, ifpossible, a high enough film build can be achieved in one pass so thatadequate hiding is ensured. If only 17 μm thickness is required in thebasecoat for black, a color which hides well, it is at least 45 μm forwhite, a color which does not hide well. Applying a film thickness likethis in one pass is still a considerable problem since the waterbornebasecoat must possess the appropriate rheological properties.

In the case of basecoats with metallic effect pigments, the previouslydescribed problem, i.e. ensuring adequate stability with a typical filmbuild of about 18 μm, is particularly prominent. Silver metallic is aparticularly critical color in this respect.

The term “rheological properties” is understood to signify that, on theone hand, the paint has such a low viscosity in the spraying process,i.e. at high shear rates, that it can be atomized easily and, on theother hand, when it strikes the substrate, i.e. at low shear rates, ithas such a high viscosity that it is sufficiently stable and does notcreate sags. The higher the layer thickness is to be, the greater theproblem of combining these contradictory properties. The creation of adefinite metallic effect is associated with these properties.

This basic problem is probably also the reason why a large number ofpublications are concerned with specially formulated binder systems orwith special additives for waterborne basecoats.

Special additives are described (EP-0 281 936) to improve rheologicalproperties and to create a better metallic effect. These are specialcoating silicates which contain substantial quantities of alkali oralkaline earth ions. These ions often lead to poor condensation waterresistance in the total system of an automobile coating because of theirhygroscopic effect.

So the paint manufacturers take pains to avoid such additives ifpossible and to use those polymers as binders which naturallyincorporate the desired properties, the so-called “tailor-made”polymers.

Among the most important representatives of this type are crosslinkedpolymer microparticles present in an aqueous dispersion, called“microgels” for short.

The addition of microgels not only brings about an improvement inrheological properties but also has a considerable effect on thestability of the paint to be applied, the alignment of the effectpigments and the adhesion of the basecoat to the primer-surfacer belowit. Thus the addition of microgels has a decisive effect on the stopchip resistance of the multilayer coating. However, it must be pointedout that not all the aforementioned properties are influenced positivelyby the addition of microgels:

Special microgels are known from EP 0 030 439 B1 and EP 0 242 235 A1.The aqueous microgel dispersions described there as beneficial formetallic finishes as well are not completely crosslinked microgels butbelong to the so-called “core/shell” microgels.

The term “core/shell structure” is understood to signify that thepolymer particle is built up essentially of two different zones: theinner zone (core) is surrounded by an outer zone (shell), where thesezones have a different chemical composition and as a result differentphysical properties as well.

The core of this microgel can be obtained from a mixture which containsdifunctional monomers in addition to monofunctional monomers. Thecrosslinking takes place through the use of an emulgator. Thiscrosslinked microparticle in accordance with EP 0 030 439 B1 issubsequently coated with a layer of non-crosslinked acrylic polymers andgrafted. According to EP 0 242 235 A1, the crosslinked microparticle iscoated with a layer of polymerizable aromatic compounds.

It is further described in EP 0 030 439 A1 to react the microgelspresent in an aqueous dispersion into a non-aqueous phase and to usethem for solvent-containing coating compositions.

From EP 0 038 127 B1, EP 0 029 637 A1 and GB 2 159 161 A microgels areknown which are obtained through polymerization of suitable monomers inthe presence of an emulgator, for example N,N-bis(hydroxyethyl)taurine.

The term “emulgator” is understood to signify those compounds which haveboth a hydrophilic and a hydrophobic residue. Emulgators bring about astabilization of emulsions, i.e. of dispersed systems of twonon-miscible or only partially miscible fluids or phases, one of whichis finely dispersed in the other. A broader definition of such compoundsis given, for example in Römpp's Encylopedia of Chemistry (vol. 2,8^(th) edition, 1981, pp. 1126-1127). Generally a distinction is madebetween ionic, non-ionic and amphoteric emulgators. For color-impartingcoating compositions, emulgators are used which have a group originatingfrom sulfonic acid as the hydrophilic residue and a longer-chain fattyalkyl residue as the hydrophobic residue.

A serious drawback to the microgels produced with the use of anemulgator is that the emulgator remains in the finished microgel; thelatter can be used only with considerable disadvantages for a largenumber of applications, for example because of the sulfur-containinggroups (sulphonic acid groups) present in the emulgator. Because of theemulgator these microgels contain, they have disadvantageous properties,for example with respect to their use in waterborne basecoats in theautomobile industry, specifically with regard to storage in water andcondensation water resistance.

EP-0 502 934 also describes a microgel dispersion. It is used both toimprove rheological properties and to increase the gassing stability ofaqueous metallic basecoats. These microgel dispersions are producedthrough single-stage aqueous phase polycondensation of a polyesterpolyol with an amino plastic resin (melamine resin).

The use of this microgel in basecoats in the painting of automobilebodies has the disadvantage that the adhesion between the basecoat and aclearcoat applied over it consisting of a powder clear coat or a powderclearcoat slurry does not meet the requirements specified by theautomobile industry.

Microgels are further known from DE 195 04 015 A1 which are produced bypolymerizing an ethylenically monofunctional compound (polyacrylate)with at least one ethylenically di- or multi-functional compound in thepresence of a polyester. The polyester functions as emulgator andstabilizer.

These microgels have the disadvantage that the rheological properties ofthese paints no longer meet the increased requirements of the automobileindustry. This is shown particularly clearly with respect to therequirements for viscosity on the one hand and stability on the other.

So it is not possible, using these microgels, to prepare an aqueousbasecoat which has a maximum viscosity of 120 mpa•s at a shear rate of1,000 s⁻¹ and is so stable that the necessary coating thicknesses of20-30 μm (depending on the particular color also less or more) can beattained without sagging.

Furthermore, microgels are known in WO 00/63265 and WO 00/63266 whichcan be obtained from a multi-stage polymerization process, in whichpolymerization of ethylenically monofunctional compounds withethylenically di- or multi-functional compounds is carried out in afirst step in the presence of a polyester polyol, polyurethane and/orpolyacrylate. As a final step, the product obtained in this way isreacted with a cross-linker. However, there has been shown to be a riskof gelling in the reaction of trimellithic acid or its anhydride withthe poly(meth)acrylate.

A further problem in the use of these subsequently crosslinked microgelsis that waterborne basecoats containing these microgels do notdemonstrate sufficient adhesion on plastic substrates to be applieddirectly to a plastic surface, an automobile bumper for example, withoutan intermediate or adhesion primer coat.

The object of the present invention is to prepare a waterborne microgelwhich can be used in waterborne basecoats, specifically for theautomobile industry, where the water-based basecoat shall demonstrate anoverall improved property level compared with water-based basecoats fromthe prior art. In accordance with a first instance in the sense of thepresent object, the multilayer coating obtainable therefrom shallovercome the previously described drawbacks of the prior art, inparticular the color coat shall have adequate adhesion on plasticsubstrates and the overall property level of the final multilayercoating shall satisfy the strict requirements of the automobilemanufacturers (particularly with respect to appearance and stone chipresistance).

In accordance with a second improvement of the overall property level inthe sense of the present object, the color coat shall be sufficientlyinsensitive to clouding and the overall property level of the finalmultilayer coating shall satisfy the strict requirements of theautomobile manufacturers (particularly with respect to appearance andstone chip resistance).

Beyond that, this microgel shall be compatible in particular withpolyurethane- and polyacrylate-based binder systems and result inparticularly high-quality coatings.

The first improvement in the sense of the object is achieved inaccordance with the invention by a emulgator-free microgel dispersed inan aqueous phase, obtainable by:

-   -   a) producing a polyacrylate (A) in the presence of at least one        compound (B) containing a phosphonic acid group, where the        polyacrylate (A) has at least one hydroxyl group and at least        one carboxyl group;    -   b) crosslinking in an aqueous phase of the reaction mixture        originating from step a) with an aminoplast resin (C);    -   c) subsequent emulsion polymerization of the reaction mixture        originating from b) with at least one monomer compound (D) which        contains at least one radically polymerizable double bond.

An emulgator-free microgel of this kind occurring in dispersion ispresent in a core/shell structure. The inner zone is completelycrosslinked in accordance with the definition given previously. Theouter zone of this core/shell microgel is not crosslinked. Crosslinkingof the outer shell when using a monomer compound with at least oneradically polymerizable double bond does not take place until bakingconditions exist for the production of corresponding multilayer coating.

Partial crosslinking in the finished paint through the outer shell isonly ensured if a monomer compound (D) containing hydroxyl groups isused with at least one radically polymerizable double bond.

Furthermore, a coating composition containing this emulgator-freemicrogel dispersion demonstrates such outstanding adhesion that it canbe used even in multilayer coating considered critical in the productionpainting of automobiles, specifically in conjunction with powderclearcoats.

If a compound without a hydroxyl group is selected as the monomer (D),the microgel obtainable in this way is crosslinked in its core, but theshell is not crosslinked and cannot be crosslinked in the paint.

Surprisingly, the use of a monomer compound (D) without hydroxyl groupsreinforces this positive adhesion property.

In accordance with this embodiment, it is ensured that the emulsionpolymeride cannot participate in the crosslinking during film formation.Outstanding adhesion on plastic substrates is achieved thereby.Outstanding adhesion is likewise achieved in conjunction with powderpaints.

Through the presence of the phosphonic acid group during reaction stepa) it is ensured that the mixture obtainable from step a) reacts in anaqueous phase with the aminoplast resin (C) in step b) to a microgeldispersion, i.e. that crosslinked particles are formed without degradingthe stability of the dispersion. Coagulation of the dispersion iseffectively avoided. In contrast to the known processes of the priorart, no trimellitic acid or its anhydride is used in all the embodimentsin accordance with the invention. These compounds have the decideddisadvantage that they considerably increase the risk of gelling duringreaction with a poly(meth)acrylate.

The reaction to the microgel in accordance with the invention ispossible independently of a normal pH value for waterborne coatingcompositions of the reaction mixture. Crosslinking independently of thedegree of neutralization is thus ensured: even with a 100% degree ofneutralization, crosslinking takes place, including with a melamineresin that is sluggish to react at low baking temperatures (i.e. of lessthan 100° C.), such as hexamethoxymethyl-melamine.

In contrast, the degree of neutralization in the production of microgeldispersions of the prior art has a considerable effect on thecrosslinking reaction: with an increasing degree of neutralization,crosslinking is reduced if not actually prevented.

As a result of the special production method for the inventive microgel,it is furthermore possible to select the required solvents in theproduction of the polyacrylate (A) or (E) in such a way that they canremain in the application-ready coating composition. The complicatedremoval of the solvents required for polymerization is dispensed withcompletely. Butyl glycol is particularly preferred as a solvent in thisconnection.

The degree of crosslinking of the microgels can be identified by theinsoluble ingredients content. The insoluble ingredients are determinedby the so-called “THF method.” For this, about 1 g of the microgeldispersion is weighed into a centrifuge tube, 10 ml of tetrahydrofuranis added and it is homogenized for about 1 minute in an ultrasound bath.Then it is centrifuged at 13,500 rpm for 15 minutes using a centrifugewith a fixed-angle rotor. The excess is subsequently carefully decantedand the tube is dried in a laboratory oven for 6 hours at 105° C. Afterthe tube has cooled, the residue is reweighed. The insoluble ingredientsare calculated using the formula below:${\%\quad{insoluble}\quad{ingredients}} = \frac{{residue}*10000}{{weighed}\quad{quantity}*\%\quad{solid}\quad{content}\quad{of}\quad{the}\quad{microgel}\quad{dispersion}}$

The term “crosslinked for the most part” refers to those microgelswhich, relative to the crosslinked part, have a ratio of non-crosslinkedpolymers of not more than 50% by weight. With respect to the core/shellmicrogel in accordance with the invention, this means that thecrosslinked core is described as “crosslinked for the most part” if itcontains not more than 50% by weight of non-crosslinked components.

The emulgator-free and phosphonic acid-modified microgel under theinvention occurs in an aqueous dispersion, lends increased structuralviscosity to compositions which contain this microgel dispersion so thatadequate stability is ensured during application, where the originatingcoating compositions can be cured both chemically and physically.

In the scope of the present invention, the property “aqueous” means thatthe dispersions under the invention contain no or only minor amounts oforganic solvents. Minor amounts are those amounts which do not destroythe aqueous nature of the dispersions under the invention.

The property “structurally viscous” means that coating compositionswhich contain this emulgator-free microgel dispersion have a viscosityat higher shear stress or a higher shear rate gradient which is lowerthan at smaller values (c.f. Römpp's Encyclopedia of Paints & PrintingInks, Georg Thieme Verlag, Stuttgart, N.Y., 1998, page 546, “Structuralviscosity”).

This structural viscosity is time-independent. This time-independencemeans that the viscosity curve, depending on shear rate, is identicalwith both increasing shear rate and with decreasing shear rate. Thisstructural viscosity behavior takes account of the needs of the sprayingapplication on the one hand and of the requirements concerning storageand settling stability on the other: In a moving state, for example whena coating composition which contains the microgels under the inventionis being pumped around the circulation line of the paint facility andwhen being sprayed, the coating composition assumes a low viscositystate which ensures good sprayability. Without any shear stress,viscosity increases and in this way ensures that the coating compositionalready on the substrate surface exhibits a reduced tendency to run onvertical surfaces (“curtaining”). In the same way, the higher viscosityin an immobile state, such as during storage, largely prevents settlingof any solid components present, such as pigments, or ensures that thesolid components which have not settled much during storage can beremixed.

Within the scope of the present invention, the term “physical curing”means the curing of one layer from a coating material by film formationas the result of the release of solvents from the coating material,where the linking within the coating takes place through chaining of thepolymer molecule film-forming components or of the binders (for thisterm see Römpp's Encyclopedia of Paints & Printing Inks, Georg ThiemeVerlag, Stuttgart, N.Y., 1998, “Binders” pages 73 and 74). Or the filmformation takes place through the coalescence of binder particles (forthis term see Römpp's Encyclopedia of Paints & Printing Inks, GeorgThieme Verlag, Stuttgart, N.Y., 1998, “Curing” pages 274 and 275).Crosslinking agents are not normally necessary for this. If necessary,the physical curing can be promoted by heat or by the effects of actinicradiation.

In contrast, the term “chemical curing” means the curing of one layer ofa coating material through a chemical reaction (see “Curing of Plastics”in Römpp's Encyclopedia of Chemistry, 8^(th) edition, 1983, pp. 1602 f).

Chemical curing is normally achieved by atmospheric oxygen or bycrosslinking agents.

The second improvement in the sense of the object of the presentinvention is achieved under the invention by an emulgator-free microgeldispersed in an aqueous phase obtainable by

-   -   a) producing a polyacrylate (A) in the presence of at least one        compound (B) having a phosphonic acid group, where the        polyacrylate (A) has at least one hydroxyl group and at least        one carboxyl group;    -   b) crosslinking in the aqueous phase of the reaction mixture        with an aminoplast resin (C) from step a);        where the reaction mixture from step b) does not undergo        subsequent emulsion polymerization.

The polyacrylate (A) originating from step a) can undergo emulsionpolymerization with at least one monomer compound (D) before step b),where monomer compound (D) contains at least one radically polymerizabledouble bond.

A coating composition containing this emulgator-free microgel dispersiondemonstrates such outstanding adhesion that it can also be used inmultilayer coatings considered critical in the production painting ofautomobiles, particularly in conjunction with powder clear coats.

In accordance with a preferred embodiment of the present invention, thepolyacrylate (A) is obtainable by polymerization

-   -   of a monomer (i) with at least one polymerizable double bond and        at least one hydroxyl group;    -   of a monomer (ii) with at least one polymerizable double bond        and at least one carboxyl group; and    -   of a monomer (iii) without hydroxyl groups and without a        carboxyl group with at least one polymerizable double bond.

As a result of the volume of monomers containing a hydroxyl group, thecrosslinking process can be stopped here. With a small volume ofmonomers containing hydroxyl groups, the crosslinking points are farapart, depending on the molecular weight of the polymers. If the volumeof monomers containing hydroxyl groups is increased, the crosslinkingpoints are grouped more tightly.

This has a positive effect on the orientation of the effect pigments,the stability and also the rheology of the coating compositioncontaining the emulgator-free microgel dispersion under the invention.

The stability of the microgel dispersion in water is positivelyinfluenced by an adequate volume of the monomer ii). However, the volumeof ii) should not be selected to be too high, otherwise its resistanceto condensation water is adversely affected.

In accordance with a further, also preferred embodiment of the presentinvention, the compound (B) is an adduct of alkylphosphonic acid with acompound containing an epoxide group.

Octylphosphonic acid can be named as an example of an alkylphosphonicacid. Adducts of glycidyl esters of a monocarbon acid branched ina-position with 5 to 18 carbon atoms per molecule with phosphonic acidcan be named as an example of compounds containing epoxide groups. Aparticularly preferred glycidyl ester is marketed under the trade nameCardura® E10 by the Resolution Company.

The choice of these initial compounds ensures pH value independenceduring crosslinking in a specially effective way.

The first improvement in the sense of the object of the presentinvention is also achieved by an emulgator-free microgel dispersed in anaqueous phase obtainable by

-   -   a) producing a polyacrylate (E) by copolymerization        -   of a monomer (i) with at least one polymerizable double bond            and at least one hydroxyl group;        -   of a monomer (ii) with at least one polymerizable double            bond and at least one carboxyl group; and        -   of a monomer (iv) with at least one polymerizable double            bond and at least one phosphonic acid group;    -   b) aqueous phase crosslinking of the reaction mixture        originating from step a) with an aminoplast resin (C);    -   c) subsequent emulsion polymerization of the reaction mixture        originating from step b) with at least one monomer compound (D)        which contains at least one radically polymerizable double bond.

Also in accordance with this embodiment, the emulgator-free andphosphonic acid-modified microgel under the invention is present in anaqueous dispersion, it endows coating compositions which contain thismicrogel dispersion with increased structural viscosity so that adequatestability is ensured during application.

The particular advantage of all emulgator-free and phosphonicacid-modified microgels under the invention in accordance with thepreviously described embodiment is that their addition to waterbornecoating compositions brings about a clear and positive improvement inspecial properties.

Basically, it can be ascertained that the rheological properties of thewaterborne coating compositions obtainable through the use of theseemulgator-free and phosphonic acid-modified microgel dispersion areimproved, compared with those of the prior art. For example, awaterborne basecoat which can be used in the automobile industry, withjust the addition of 20% of the emulgator-free microgel dispersion underthe invention—relative to the solids content of the coatingcomposition—shows a viscosity of at most 100 mPa•s at a shear rate of1,000 s⁻¹, where the dry film thickness of the cured basecoat measures22 μm without any sags being observed.

The emulgator-free and phosphonic acid-modified microgel under theinvention is especially suitable in the production and formulation ofwaterborne basecoats, in particular for those that are used in theautomobile industry.

In addition, the emulgator-free and phosphonic acid-modified microgeldispersion under the invention gives the color-imparting coatingcomposition outstanding adhesion on plastic substrates.

This property deserves special emphasis since this paint can be used inan unchanged formulation for metal, pretreated substrates (automobilebodies) as well as for plastic add-on parts for automobiles (e.g.bumpers). This prevents color deviation. Until now it has often beennecessary in the area of industrial applications, starting withwaterborne basecoats for the production painting of automobile bodies,to increase their adhesion on plastic substrates by the addition ofspecific “adhesion promoters” or even through additional adhesion coats.

The outstanding adhesion of the basecoats containing the microgel underthe invention can be seen from the “steam jet test,” which is the testused in the automobile industry for satisfactory adhesion.

Furthermore, through the addition of the emulgator-free and phosphonicacid-modified microgel dispersion under the invention to color-impartingcoating compositions the overall property level of the final multilayercoating is not negatively affected. The final multilayer coating showsexcellent properties with respect to mechanical (stone chip resistance)and visual criteria (i.e. orientation of the effect pigments).

Further it can ascertained that the emulgator-free and phosphonicacid-modified microgel dispersions under the invention have excellentworkability with binder systems based on polyurethanes, polyacrylates ormixtures of polyurethanes and polyacrylates. This good workability isshown particularly from the good adhesion properties of the originatingpaint film on plastic substrates. Coating compositions combiningpolyurethane- and/or polyacrylate-based binder systems and theemulgator-free microgel dispersion under the invention produce extremelyhigh-quality coatings.

The object of the present inventions is also achieved by anemulgator-free microgel dispersed in an aqueous phase obtainable by

-   -   a) producing a polyacrylate (E) by copolymerization        -   a. of a monomer (i) with at least one polymerizable double            bond and at least one hydroxyl group;        -   b. of a monomer (ii) with at least one polymerizable double            bond and at least one carboxyl group; and        -   c. of a monomer (iv) with at least one polymerizable double            bond and at least one phosphonic acid group;    -   b) aqueous phase crosslinking of the reaction mixture        originating from step a) with an amino plastic resin (C);        where the reaction mixture originating from step b) does not        undergo any subsequent emulsion polymerization.

The polyacrylate (A) originating from step a) can undergo emulsionpolymerization before step b) with at least one monomer compound (D)which contains at least one radically polymerizable double bond.

Also in accordance with this embodiment, the emulgator-free andphosphonic acid-modified microgel under the invention is present in anaqueous dispersion, and endows coating compositions containing thesemicrogel dispersions with increased structural viscosity so thatadequate stability is ensured during application.

The particular advantage of all emulgator-free and phosphonicacid-modified microgels under the invention in accordance with thepreviously described embodiment is that their addition to water-reducedcoating compositions brings about a clear and positive improvement inspecial properties.

Basically it can be ascertained that the rheological properties of thewaterborne coating compositions obtainable through the use of theseemulgator-free and phosphonic acid-modified microgel dispersion areimproved, compared with those of the prior art. For example, awaterborne basecoat which can be used in the automobile industry, withjust the addition of 20% of the emulgator-free microgel dispersion underthe invention—relative to the solids content of the coatingcomposition—shows a viscosity of at most 100 mPa•s at a shear rate of1,000 s⁻¹, where the dry film thickness of the cured basecoat measures22 μm without any sags being observed.

The emulgator-free and phosphonic acid-modified microgel under theinvention is especially suitable in the production and formulation ofwaterborne basecoats, in particular for those used in the automobileindustry.

Furthermore the emulgator-free and phosphonic acid-modified microgelunder the invention lends the color-imparting coating compositionoutstanding application stability, particularly with respect toresistance to clouding.

Moreover, through the addition of the emulgator-free and phosphonicacid-modified microgel dispersion under the invention to color-impartingcoating compositions the overall property level of the final multilayercoating is not negatively affected. The final multilayer coating showsexcellent properties with respect to mechanical influences (stone chipresistance).

It can be further ascertained that the emulgator-free and phosphonicacid-modified microgel dispersions under the invention has excellentworkability with binder systems based on polyurethanes, polyacrylates ormixtures of polyurethanes and polyacrylates. This good workability canbe seen particularly from the good adhesion properties of theoriginating paint film on plastic substrates. Coating compositions froma combination of polyurethane- and/or polyacrylate-based binder systemsand the emulgator-free microgel dispersion under the invention produceextremely high-quality coatings.

In a further, also preferred embodiment of the present invention,copolymerization is carried out in the presence of an additional monomer(iii) without a hydroxyl group and without a carboxyl group which has atleast one polymerizable double bond.

As a result of the volume of monomers containing hydroxyl groups, thecrosslinking process can be stopped here. With a small volume ofmonomers containing hydroxyl groups, the crosslinking points are farapart, depending on the molecular weight of the polymers. If the volumeof monomers containing hydroxyl groups is increased, the crosslinkingpoints are grouped more tightly.

This has a positive influence on the orientation of the effect pigments,the stability and also the rheology of the coating compositioncontaining the emulgator-free microgel dispersion under the invention.

The monomer (i) can be selected from the hydroxyalkyl esters of acrylicacid, methacrylic acid or another α,β-olefinically unsaturatedcarboxylic acid which are derived from an alkylene glycol estered withthe acid, or which can be obtained through reaction of theα,β-olefinically unsaturated carboxylic acid with an alkylene oxide suchas ethylene oxide or propylene oxide, in particular hydroxyalkylestersof acrylic acid, methacrylic acid, ethacrylic acid, crotonic acid,maleic acid, fumaric acid or itaconic acid, in which the hydroxylalkylgroup contains up to 20 carbon atoms, such as 2-hydroxyethylacrylate,2-hydroxypropylacrylate, 3-hydroxypropylacrylate,3-hydroxybutylacrylate, 4-hydroxybutylacrylate, 4-hydroxymethacrylate,4-hydroxyethacrylate, 4-hydroxycrotanate, 4-hydroxymaleinate,4-hydroxyfumarate or 4-hydroxyitaconate; or hydroxycycloalkylesters suchas 1,4-bis(hydroxymethyl)cyclohexaneacrylate, octahydro-4,7-methano-1H-inden-dimethanolacrylate or methylpropanediolmonoacrylate,methylpropanemonomethacrylate, methylpropanemonoethacrylate,methylpropanemonocrotonate, methylpropanemonomaleinate,methylpropanemonofumarate, or methylpropanemonoitaconate.

Conversion products from cyclic esters, such as ε-caprolactam, and thepreviously described hydroxyalkyl or cycloalkyl esters (obtainable forexample under the name Tone® M 100 from DOW Chemicals) can be used.

Preferably the monomer (i) is selected from the group ofhydroxyethyl(meth)acrylate, hydroxypropyl(meth)acrylate,hydroxybutyl(meth)acrylate and ε-caprolactam estered on ahydryoxy(meth)acrylate base.

The monomer (ii) can be selected from the group of acrylic acid,methacrylic acid, ethacrylic acid, crotonic acid, maleic acid, fumaricacid or itaconic acid. Preferably the monomer (ii) is selected from thegroup of acrylic acid and methacrylic acid.

Regarding monomer (iii) it can be

-   -   Vinylaromatic compounds, such as vinyltoluene, a-methyl styrene,        p-, m- or p-methylstyrene, 2,5 dimethylstyrene,        p-methoxystyrene, p-tert.-butyl styrene, p-dimethylaminostyrene,        p-acetamidostyrene, and m-vinyl phenol, specifically preferred        styrene;    -   Esters of acrylic or methacrylic acid, such as        methyl(meth)acrylate, ethyl(meth)acrylate, butyl(meth)acrylate,        iso-butyl(meth)acrylate, ter.-butyl(meth)acrylate,        isopropyl(meth)acrylate, pentyl(meth)acrylate,        isoamyl(meth)acrylate, hexyl(meth)acrylate,        α-ethylhexyl(meth)acrylate, furfuryl(meth)acrylate,        octyl(meth)acrylate, 3,5,5-trimethylhexyl(meth)acrylate,        decyl(meth)acrylate, lauryl(meth)acrylate,        hexadecyl(meth)acrylate, octadecyl(meth)acrylate,        stearyl(meth)acrylate and ethyltriglycol(meth)acrylate;        cyclohexyl(meth)acrylate, isobornyl(meth)acrylate;    -   Aminoethylacrylate, aminoethylmethacrylate, allylamine,        N-methyliminoethylacrylate or tert. butylaminoethylmethacrylate;    -   N,N-Di(methoxymethyl)aminoethylacrylate or -methacrylate or        N,N-Di(butoxymethyl)aminopropylacrylate or -methacrylate;    -   (Meth)acrylic acid amides such as (meth)acrylic acid amide,        N-methylacrylic acid amide, N-methylol acrylic acid amide,        N,N-dimethylolacrylic acid amide, N-methoxymethylacrylic acid        amide, N,N-di(methoxymethyl)acrylic acid amide,        N-ethoxymethylacrylic acid amide and/or        N,N-di(ethoxyethyl)-(meth)acrylic acid amide;    -   Acryloyloxy- or methacryloyloxyethyl-, propyl- or butylcarbamate        or -allophanate; other example of suitable monomers containing        carbamate groups are described in U.S. Pat. Nos. 3,479,328,        3,674,838, 4,126,747, 4,279,833 or 4,340,497;    -   Monomers containing epoxide groups such as the glycidyl ester of        acrylic acid, methacrylic acid, ethacrylic acid, crotonic acid,        maleic acid, fumaric acid or itaconic acid or        allylglycidylether;    -   Ethylenically di- or multi-functional compounds, preferably        diacrylates, triacrylates, and/or (meth)acrylic acid esters of        polyfunctional alcohols, specifically allyl(meth)acrylate,        hexane dioldi(meth)acrylate, ethylene glycol di(meth)acrylate,        neopentyl glycol di(meth)acrylate, butane dioldi(meth)acrylate        or trimethyl propane tri(meth)acrylate.

Preferably the monomer (iii) is selected from the group of the hydroxylgroup-free acryl(meth)acrylic acid esters and styrene.

Preferably monomer (iv) is vinyl phosphonic acid.

Examples of aminoplast resins are described, for example in Römpp'sEncyclopedia of Paints & Printing Inks, Georg Thieme Verlag, 1998, page29, “Amino resins”: the textbook Paint Additives by Johan Bieleman,Wiley-VCH, Weinheim, N.Y., 1998, pages 242 ff, the book Paints, Coatingsand Solvents, 2^(nd) completely revised edition, edit. D. Stoye and W.Freitag, Wiley-VCH, Weinheim, N.Y., 1998, pages 80 ff, the patents U.S.Pat. No. 4,710,542 A or EP 0 245 700 A1 and in the article by B. Singhand colleagues “Carbamylmethylated Melamines, Novel Crosslinkers for theCoatings Industry,” in Advanced Organic Coatings Science and TechnologySeries, 1991, vol. 13, pages 193 to 207.

The aminoplast resin is preferred, a melamine resin as marketed, forexample, under the trade name Cymel® 327 by the Cytec Company.

In accordance with an additional, similarly preferred embodiment of thepresent invention, the monomer compound (D) used in the emulsionpolymerization in step c) has at least one hydroxyl group.

An emulgator-free microgel of this type present in dispersion occurs ina core/shell structure. The inner zone in accordance with the definitionpreviously given is completely crosslinked. The outer zone of thiscore/shell microgel is not crosslinked. Crosslinking of the outer shellwhen using a monomer compound with at least one radically polymerizabledouble bond does not take place until baking conditions exist for theproduction of corresponding multilayer coatings.

Partial crosslinking in the finished paint through the outer shell isonly ensured when a monomer compound containing hydroxyl groups with atleast one radically polymerizable double bond is used.

In accordance with this embodiment, the polymerized monomer mixture doesnot participate in the crosslinking to the microgel.

Furthermore, a coating composition containing this emulgator-freemicrogel dispersion demonstrates such outstanding adhesion that it canbe used even in multilayer coatings considered critical in theproduction painting of automobiles, specifically in conjunction withpowder clearcoats.

In the case of the previously described core/shell polymers ormicrogels, in accordance with a preferred embodiment the emulsionpolymerization is carried out in the presence of an additional monomercompound (D) which contains at least one radically polymerizable doublebond and no hydroxyl groups.

An emulgator-free microgel of this type present in dispersion occurs ina core/shell structure. The inner zone is completely crosslinked, inaccordance with the description given previously. The outer zone of thiscore/shell microgel is similarly not crosslinked. In contrast to thecore/shell polymer previously described, no crosslinking of the outershell can take place under baking conditions for the production ofcorresponding multilayer coatings.

In accordance with this embodiment, it is ensured that the emulsionpolymeride cannot participate in the crosslinking during film formation.Outstanding adhesion on plastic substrates or under powder clearcoats isthereby achieved.

In accordance with a similarly preferred embodiment of the presentinvention, the microgel has an acid number between 10 and 45 mg KOH/g,specifically between 10 and 30 mg KOH/g.

This ensures adequate stability of the dispersion in water.

From a methodological point of view, this polymerization does notexhibit any unusual features but takes place following the usual andknown methods of radical emulsion polymerization in the presence of atleast one polymerization initiator.

Examples of suitable polymerization initiators are initiators formingfree radicals such as dialkyl peroxides, such as di-tertiary-butylperoxide or dicumylperoxide; hydroperoxides such as cumolhydroperoxideor tertiary-butylhydroperoxide; peresters such tertiarybutylperbenzoate, tertiary-butylperpivalate,tertiary-butylper-3,5,5-trimethyl-hexanoate ortertiary-butylper-2-ethylhexanoate; potassium, sodium or ammoniumperoxodisulfate; azodinitriles such as azobisisobutyronitrile;c-c-splitting initiators such benzpinakolsilylether; or a combination ofa non-oxidizing initiator with hydrogen peroxide. Water-insolubleinitatiors are preferably used. The initiators are preferably used in avolume of 0.1 to 25% by weight, especially preferred of 0.75 to 10% byweight, relative to the total weight of the monomers (a).

One possibility is the initiation of polymerization through a redoxsystem. This process, well known in emulsion polymerization engineering,utilizes the fact that hydroperoxides are stimulated to radical decay atvery low temperatures by suitable reduction agents.

Suitable reduction agents are, for example, sodium metabisulfite or itsformaldehyde additive product (Na-hydroxymethanesulfinate). Isoascorbicacid is also highly suitable. The combination oftertiary-butylhydroperoxide, (iso)ascorbic acid and iron(II)sulfate isespecially advantageous.

Using this mixture has the advantage that polymerization can beinitiated at room temperature.

The corresponding monomers are polymerized in the solutions or theaqueous emulsions with the aid of the aforementioned radical-forminginitiators at temperatures of 30 to 95° C., preferably 40 to 95° C., andwhen redox systems are used, at temperatures of 35 to 90° C. Inoperations under pressure, the emulsion polymerization can also becarried out at temperatures above 100° C.

The same applies to solution polymerization when higher-boiling organicsolvents and/or pressure is used.

It is preferred that feed of the initiator is started some time,generally about 1 to 15 minutes, before the feed of the monomers.Further, a process is preferred in which addition of the initiatorbegins at the same time as addition of the monomers and ends about ahalf hour after the addition of the monomers has ended. The initiator ispreferably added at a constant volume per unit of time. After theaddition of the initiator is concluded, the reaction mixture ismaintained at polymerization temperature long enough (generally 1 to 1½hours) for all the monomers being used to have been essentiallycompletely reacted. “Essentially completely reacted” is intended tosignify that preferably 100% by weight of the monomers used have beenreacted, but that it is still possible that a small residual monomercontent, at most up to 0.5% by weight relative to the weight of thereaction mixture, can remain unreacted.

The customary and known stirrer vessels, stirrer vessel cascades, tubeflow reactors, loop reactors or Taylor reactors, as described in patentDE 10 71 241 B1, patent applications EP 0 498 583 A1 or DE 198 28 742 A1or in the article by K. Kataoka in Chemical Engineering Science, vol.50, number 9, 1995, pages 1409 to 1416, can be considered as reactorsfor graft polymerization.

The previously described emulgator-free microgel dispersion is suitableunder the invention for producing a multilayer coating, in particular inthe automobile industry.

Quite especially preferred is the use of the emulgator-free microgeldispersion in the color-imparting coating composition, i.e. in abasecoat.

The best results with respect to rheological, mechanical and visualproperties are achieved when the amount of microgel, relative to thesolids in the coat obtained therefrom, is between 20 and 85%, preferablybetween 20 and 65%.

It is surprising that the emulgator-free microgel dispersions under theinvention can be used in addition to the usual coating silicates inwaterborne basecoat paints. In this case, the paint films originatingtherefrom do not exhibit inadequate condensation water resistancecompared with basecoat paints without the addition of the inventivemicrogel dispersion.

For use in accordance with the invention, the multilayer coating canconsist of three different layers, i.e. of

-   -   1) a first layers on the electrically conductive substrate        consisting of an electrophoretically deposited coating agent;    -   2) a second, color-imparting layer, obtainable from a waterborne        coating composition, which contains the emulgator-free microgel        dispersion from the invention; and    -   3) a third clearcoat layer.

In the case of this multilayer coating of specifically only threedifferent layers it must be stressed that the originating multilayercoating also has adequate stone chip resistance which can be attributedto the special properties of the waterborne basecoat paint containingthe emulgator-free microgel of the present invention.

It is also possible that the multilayer coating consists of fourdifferent layers, i.e. of

-   -   1) a first layer on the electrically conductive substrate        consisting of an electrophoretically deposited coating agent;    -   2) a second layer consisting of a primer or a filler;    -   3) a third, color-imparting layer, obtainable from a waterborne        coating composition, which contains the emulgator-free microgel        dispersion from the invention; and    -   4) a fourth clearcoat layer.

An advantage of this four-stage system is that the cured color-impartinglayer has a further positive effect on the stone chip resistanceproperties of the primer-filler layer.

By using the emulgator-free microgel in accordance with the invention, aconsiderably higher film build—relative to conventional basecoatpaints—can be achieved. The thickness of the cured coat from a coatingcomposition containing the emulgator-free microgel dispersion inaccordance with the invention may be between 15 and 55 μm.

The electrophoretically deposited coating agents are water-based coatingcompositions with a solids content of about 10 to 20% by weight, whichnormally carry binders, ionic groups or substitutes which can be reactedto ionic groups, and groups capable of chemical crosslinking, andcontain in addition pigments and other normal additives.

Examples of such electrodeposition paints are described in DE 28 24 418A1 , DE 33 24 211 A1, EP 0 082 291, EP 0 178 531, EP 0 227 975, EP 0 234395, EP 0 245 786, EP 0 261 385, EP 0 310 971, EP 0 333 327, EP 0 414199, EP 0 456 270, EP 0 476 514, and U.S. Pat. No. 3,922,253.

The clearcoat layer, which in a multilayer coating for automobiles islocated above the color-imparting basecoat layer, may be obtained byapplying and baking a conventional solvent-borne or waterborne clearcoatcomposition, which is available as a single-component or two-componentmixture and which contains one or more basic resins as the film-formingbinder. To the extent that the binders are not self-crosslinking, theclearcoat composition may also contain cross-linkers. Polyester,polyurethane and/or poly(meth)acrylate resins, for example, can be usedas the film-forming binders (base resins).

In addition to the chemically crosslinking binders and any necessarycross-linkers, these clearcoat paints may contain normal additives, suchas catalysts, leveling agents and UV protective agents.

Examples of solvent-borne clearcoat compositions in single-component ortwo-component mixtures are described in DE 38 26 693 A1, DE 40 17 075A1, DE 41 24 167 A1, DE 41 33 704A1, DE4204518A1, DE4204611 A1,EP0257513, EP0408858, EP0 523 267 A and EP 0 557 822.

Examples of waterborne clearcoat compounds in single-component ortwo-component form are described in DE 39 10 829 A1, DE 40 09 931 A1, DE40 09 932 A1, DE 41 01 696 A1, DE 41 32 430 A1, DE 41 34 290 A1, DE 4203 510 A1, EP 0 365 098, EP 0 365, 775, EP 0 469 079 and EP 0 546 640,particularly in DE 44 19 216 A1 and DE 44 42 518 A1.

The clearcoat layer can also be produced from a powder paint or a powderclearcoat slurry. Reference is made to DE 42 22 194 A1, DE 42 27 580 A1,EP 0 509 392, EP 0 509 393, EP 0 522 648, EP 0 544 206, EP 0 555 705, EP0 652 265, EP 0 666 779 and EP 0 714 958 with respect to the powderclearcoat or the powder clearcoat slurry.

It is also possible to react the microgel dispersion under the inventioninto a non-aqueous phase and to use it in solvent-borne coatingcompositions.

To obtain microgels in a non-aqueous phase, the water must be removedfrom the microgels in accordance with the invention present in anaqueous phase.

This can be done through any known process, for example, by spraydrying, freeze drying or condensation, if necessary under reducedpressure.

After the water has been removed, the microgel of the invention may bepresent in powder form or as a resinous mass.

In accordance with a preferred variation, the microgel present in anaqueous phase can be reacted into a fluid, organic phase. This can bedone by azeotropic distillation. One possible procedure is for theaqueous, emulgator-free microgel dispersion to be fed at increasedtemperature, if necessary at reduced pressure, continuously ordiscontinuously into a reactor which contains a retarder, i.e. a solventor a mixture of several solvents of which at least one forms anazeotrope with water.

The reactor is equipped with a suitable condensation device and a waterseparator with a return to the reactor. After the azeotrope reachesboiling temperature, the gaseous azeotropic phase (i.e. retarder andwater) rises in the condensation device. The azeotrope condenses thereand runs into the water separator. A phase separation between theretarder and the water takes place in the separator. In continuousazeotropic distillation, the retarder returns to the reactor so thatonly small quantities of retarder have to be used. The water obtainedfrom the separator is free of organic constituents and can be used againto produce the aqueous microgel dispersion in accordance with theinvention.

The retarder can be selected from the group of xylol, butylacetate,methylisobutylketone, methylamylketone, pentanol, hexanol orethylhexanol.

A considerable advantage in this process is that after the retarder hasbeen reacted to the organic phase, it remains there and is beneficialfor the use of solvent-borne coating compositions. With respect to thefurther use of these microgels present in an organic phase for theproduction of solvent-containing coating compositions, the retardersmentioned are suitable solvents.

Because the retarder is recycled and water simultaneously accumulateswith no additional process steps, this process is remarkable for itsextraordinary degree of environmental compatibility, since no byproductsrequiring disposal are created. Said byproducts accumulate in largequantities with comparable known production processes.

A special form of azeotropic distillation is carried out in such a waythat the aqueous, emulgator-free microgel dispersion is added to amixture of a retarder and a high-boiling organic solvent. Thishigh-boiling, organic solvent prevents the microgels from being bakedonto the wall of the reactor during reaction to the organic phase.

The high-boiling solvent can be selected from the group of glycolesters, such as butyl glycol acetate and/or butyl diglycol acetate.

As in the case of the retarder, the high-boiling solvent is also anormal component in a coating composition containing solvents.

The microgel obtainable in this way can be used in particular forcoating compositions containing solvents.

A preferred application of the invention is its use in basecoat paintscontaining solvents, in particular effect basecoats and clearcoats forthe topcoating or finishing of automobiles. This microgel present in anaqueous phase similarly endows these solvent-containing coatingcompositions with excellent application characteristics and outstandingdecorative properties which are exhibited, for example, in a distinctivemetallic effect, very good resistance to sagging on vertical surfaces(SCA—sagging control agent), freedom from clouding, resistance toresoftening from the clearcoat, good filling of sanding marks andsatisfaction of the standard automobile industry requirements for paintproperties.

The microgels can be used equally well for the production ofsolvent-containing clearcoats, coil coating compositions and bakeablepaints for industrial applications and house paints for the constructionsector.

A further unique feature of this microgel is found in its highresistance to shear. This property allows such microgels to be used forthe first time in the production of pigment preparations, in particularas mulling agents for tinting pastes. The advance here is that thetinting pastes produced in this way have a high pigment content and lowviscosity at the same time.

EXAMPLES

Producing the Initial Products

Acrylate Dispersion 1:

305 g of butyl glycol is weighed in a 2-liter reaction vessel with astirrer and a feed vessel and heated to 120° C. At 120° C., a mixture of40 g of styrene, 53.3 g of butylmethacrylate, 462.3 g of laurylacrylate,152.4 g of 2-hydroxyethylacrylate, 6.5 g vinyl phosphonic acid, 41.6 gof acrylic acid and 15,1 g of tertiary-butylper-2-ethylhexanoate isdosed at an even rate from the feed vessel in the space of 2 hours.After the feed is completed, it is repolymerized for 0.5 hour. Then amixture of 7.2 g butyl glycol and 1.5 g oftertiary-butylper-2-ethyl-hexanoate is added in the space of 0.1 hour.After the feed is completed, it is repolymerized for 1.5 hours.

Then a mixture of 14.3 g dimethylethanolamine and 970 g of deionizedwater is added. A stable dispersion with a solids content of 36% isobtained (30 minutes at 180° C.).

Acrylate Dispersion 2:

300 g of butyl glycol is weighed in a 2-liter reaction vessel with astirrer and a feed vessel and heated to 120° C. At 120° C., a mixture of146.4 g of 2-ethylhexacrylate, 120 g of styrene, 160 g of butylmethacrylate, 255.2 g of polypropylene glycol monomethacrylate with anumber-average molecular weight of 350, 105 g of 4-hydroxybutylacrylate,7.2 g of vinyl phosphonic acid, 46.2 g of acrylic acid and 23.2 g oftertiary-butylper-2-ethylhexanoate is evenly dosed from the feed vesselin the space of 3 hours. After the feed is completed, it isrepolymerized for 0.5 hour. Then a mixture of 7.2 g butyl glycol and 1.5g of tertiary-butylper-2-ethylhexanoate is added in the space of 0.1hour. After the feed is completed, it is repolymerized for 1.5 hours.

Then a mixture of 18.7 g of dimethylethanolamine and 850 g of deionizedwater is added. A stable dispersion with a solids content of 41% isobtained (30 minutes at 180° C.).

Acrylate Dispersion 3:

300 g of butyl glycol is weighed in a 2-liter reaction vessel with astirrer and a feed vessel and heated to 100° C. At 100° C., a mixture of576.6 g 2-ethylhexyl acrylate, 210 g of 4-hydroxybutyl acrylate, 7.2 gof vinyl phosphonic acid and 46.2 g of acrylic acid is evenly dosed fromthe feed vessel in the space of 3 hours. A mixture of 25.2 gtert.-butylper-2-ethylhexanoate and 48 g of butyl glycol is added from asecond feed vessel in the space of 3.5 hours. Both feeds are startedsimultaneously. After the second feed is completed, it is repolymerizedfor 2 hours.

Then 18.1 g of dimethylethanolamine and 800 g of deionized water isadded. A stable dispersion with a solids content of 41% is obtained (30minutes at 180° C.).

Acrylate Dispersion 4:

305 g of butyl glycol are weighed in a 2-liter reaction vessel with astirrer and a feed vessel and heated to 100° C. At 100° C., 10 percentby weight of a mixture of 257.8 butyl acrylate, 54 g of styrene, 72 g ofbutyl methacrylate, 229.7 g of polypropylene glycol monomethacrylatewith a number-average molecular weight of 350, 94 g of 4-hydroxy butylacrylate, 6.5 g of vinyl phosphonic acid, 41.6 g of acrylic acid and15.1 g of tertiary-butylper-2-ethylhexanoate is added from a feedvessel. After 20 minutes the remaining 90 percent by weight of themixture is dosed evenly in the space of 3 hours. After the feed iscompleted, it is repolymerized for 0.5 hour. Then a mixture of 7.2 gbutyl glycol and 0.8 g of tertiary-butylper-2-ethylhexoanate is dosed inthe space of 0.1 hour. After this feed is completed, it is repolymerizedfor 2 hours.

Then a mixture of 15.4 g of dimethylethanolamine and 1590 of deionizedwater is added. A stable dispersion with a solids content of 28% isobtained (30 minutes at 180° C.).

Acrylate Dispersion 5 (for Application Example):

200 g of butyl glycol is weighed in a 4-liter reaction vessel with astirrer and a feed vessel and heated to 120° C. At 120° C., a mixture of285 g of methylmethacrylate, 140 g of 2-ethylhexylacrylate, 60 g of2-hydroxypropylmethacrylate, 15 g of methylacrylic acid and 10 gtertiary-butylper-2-ethylhexanoate is evenly dosed in the space of 3hours. After the feed is completed, it is repolymerized for 0.5 hour.Then a mixture of 10 g butyl glycol and 1 g oftertiary-butylper-2-ethylhexanoate is dosed in the space of 0.1 hour.After this feed is completed, it is repolymerized for 1.5 hours.

Then 15.5 g of dimethylethanolamine and 1630 g of deionized water areadded. A stable dispersion with a solids content of 22% is obtained (30minutes at 180° C.).

Polyurethane Dispersion 1:

602.3 g of a polyester with a number-average molecular weight of 1440 ona dimerized sebaceous acid base (Pripol® 1013 from Unichema) and1.6-hexanediole with an acid number below 3, 56 g dimethylpripione acid,306.2 g tetramethylxylylenediisocyanate, 241 g methylethylketone and 0.9g dibutylinndilaurate are weighed in a 6-liter reaction vessel withreturn condenser. This mixture is maintained at 80° C. until theisocyanate content amounts to 2.35%. Then 90.4 g trimethylolpropane and23 g methylethylketone are added and pushed to an isocyanate content of<0.03% at 80° C. Then a mixture of 33.5 g dimethylethanolamine and 1085g deionized water and afterward 1598 g deionized water are added.Following vacuum distillation, in which the methylethylketone isremoved, a dispersion with a solids content of 28% is obtained (60minutes at 120° C.).

Polyurethane Dispersion 2 (for Application Example):

249.4 g of a polyester with a number-average molecular weight of 2100 ona 1.6-hexanediole and isophthalic acid base, 15.9 g dimethylolpropionicacid, 86.9 g tetramethylxylylenediisocyanate, 0.2 g dibutyltindilaurateand 117.2 g methylethylketone are weighed in a 4-liter reaction vesselwith a return condenser and heated to 85° C. This mixture is maintainedat 85° C. until the isocyanate content reads 1.95 %. Then 76.8 g of adi-trimethylolpropane monolaurin acid ester is added and pushed to anisocyanate content of<0.02% at 85° C. Then a mixture of 10.7 gdimethylethanolamine and 1080 g of deionized water is added. Followingvacuum distillation, in which the methylethylketone is removed, adispersion with a solids content of 29% is obtained (60 minutes at 120°C.).

Polyester Dispersion 1 (for Application Example):

332.8 g of neopentyl glycol, 283.2 g of hexane diole, 696 g of adimerized fatty acid (Pripol® 1013 from Unichema) and 184.2 g ofhexahydrophthal acid anhydride is weighed in a 4-liter reaction vesselwith stirrer and packed column and heated so that column headtemperature does not exceed 100° C. Maximum esterization temperature is230° C. At an acid number below 10, it is cooled. At 150° C., 307.2 g oftrimellitic acid anhydride is added and heated so that the column headtemperature does not exceed 100° C. Maximum esterization temperature is180° C. At an acid number of 30, it is cooled. A polyester with acalculated molecular weight of 1870 and a hydroxyl number of 83 isobtained.

At a temperature below 100° C., a mixture of 42.7 g dimethylethanolamineand 1380 g deionized water is dosed in a controlled manner and afterward1910 g of deionized water is added. A stable dispersion with a solidscontent of 30% is obtained (60 minutes at 120° C.).

Production of the Microgel Dispersions Under the Invention

Microgel Dispersion 1:

834.7 g of acrylate dispersion 1 is weighed in a 2-liter reaction vesseland while stirring 139.9 g of a standard melamine resin (Cymel® fromDyno Cytec), 1 g of dimethylethanolamine and 580 g of deionized waterare added in succession to the initial mixture. It is heated to 95° C.and condensed for 7 hours at 95° C., following which it is cooled and 14g of dimethylethanolamine is added to the initial mixture.

A stable dispersion with a solids content of 24% is obtained (30 minutesat 180° C.). A sample of this dispersion reduced with tetrahydrofuranexhibits severe turbidity.

Microgel Dispersion 2:

830.7 g of acrylate dispersion 2 is weighed in a 2-liter reaction vesseland while stirring 162.3 g of a standard melamine resin (Cymel® fromDyno Cytec) and 800 g of deionized water are added in succession to theinitial mixture. It is heated to 94° C. and condensed for 10 hours at94° C., following which it is cooled and 11.9 g of dimethylethanolamineis added to the initial mixture. A stable dispersion with a solidscontent of 24% is obtained (30 minutes at 180° C.). A sample of thisdispersion reduced with tetrahydrofuran exhibits severe turbidity.

Microgel Dispersion 3:

830.7 g of acrylate dispersion 3 is weighed in a 4-liter reaction vesselwith a return condenser and while stirring 162.3 g of a standardmelamine resin (Cymel® from Dyno Cytec), and 800 g of deionized waterare added in succession to the initial mixture. This mixture is heatedto 94° C. and maintained at 94° C. for 10 hours. Then 11.7 g ofdimethylethanolamine is added to the initial mixture. Afterward amixture of 15.9 g styrene, 23.7 g of butylmethacrylate, 14.5 g of4-hydroxybutylacrylate and 1.9 g of tertiary-butylper-2-ethylhexanoateis added at 90° C. After one hour at 90° C., a mixture of 0.4 gtertiary-butylper-2-ethylhexanoate and 2 g of butyl glycol is added,heated to 95° C. and repolymerized for 2 hours at 95° C. After coolingand the addition of 330 g of deionized water, a stable dispersion with asolids content of 22% is obtained (30 minutes at 180° C.). A sample ofthis dispersion reduced with tetrahydrofuran exhibits severe turbidity.

Microgel Dispersion 4:

847.9 g of acrylate dispersion 4 is weighed in a 2-liter reaction vesselwith return condenser and while stirring 115 g of a standard melamineresin (Cymel® 327 from Dyno Cytec) and 400 g of deionized water areadded in succession to the initial mixture. This mixture is heated to97° C. and maintained at 97° C. for 9 hours. After cooling and theaddition of 7.7 g of dimethylethanolamine, a stable dispersion with asolids content of 22% is obtained (30 minutes at 180° C.). A sample ofthis dispersion reduced with tetrahydrofuran exhibits severe turbidity.

Microgel Dispersion 5:

194 g of deionized water and 200 g of microgel dispersion 4 are weighedin a 2-liter reaction vessel with return condenser and while stirringheated to 82° C. At 82° C., a mixture of 30 g of methylmethacrylate,46.4 g of laurylacrylate, 2.4 g of acrylamide, 1.6 g of2.2′-azo-bis-isobutyronitrile (AIBN), 350 g of microgel dispersion 4 and55 g of deionized water is added and repolymerized for 3 hours at 82° C.After cooling and the addition of 0.7 g of dimethylethanolamine, astable dispersion with a solids content of 23% is obtained (30 minutesat 180° C.). A sample of this dispersion reduced with tetrahydrofuranexhibits severe turbidity.

Use of the Microgel Dispersions Under the Invention

Application Example 1

To produce a metallic water-based paint, 107.1 g of polyurethanedispersion 1 and 312.5 g of the microgel dispersion 1 under theinvention, a mixture of 50 g polyester dispersion 1, 0.4 g ofdimethylethanolamine and 35 g of deionized water, 16.6 g of a standardmelamine resin (Cymel® 327 from Dyno Cytec), 42.9 g of a standardaluminum bronze, previously stirred to a paste in 56.2 g of butyl glycoland 31.6 g of n-Butanol and a mixture of 20.2 g of a standard acrylatethickener (Latekoll® D from BASF) and 46 g of deionized water areprocessed into a paint. The pH value is adjusted to 8.00 to 8.30 withdimethylethanolamine and to a viscosity of 100 mPa•s with deionizedwater (measured at 1,000 s⁻¹).

Application Example 2

The same procedure is followed as in example 1. However, the 312.5 g ofmicrogel dispersion 1 is replaced by 312.5 g of microgel dispersion 2under the invention.

Visual Check:

The aqueous basecoats produced in accordance with the examples 1 and 2described previously are applied by spraying onto a 70×70 cm metal platein a climate-controlled spray booth so that a dry coating thickness of15-18 μm is obtained. After flashing for 5 minutes, each of the paintedsubstrates receives a standard automobile production clearcoat with adry coating thickness of 40-45 μm and the coatings are then baked for 30minutes at 140° C.

Through the use of the microgel dispersions under the invention,finishes are obtained which are remarkable for their very good aluminumflake orientation, a substantially reduced tendency to clouding and anoutstanding topcoat condition.

Application Example 3

To produce a metallic water-based paint, 93.1 g of polyurethanedispersion 2, 245.5 g of microgel dispersion 3 under the invention,165.5 g of acrylate dispersion 5, 19.4 g of a standard melamine resin(Cymel® 327 from Dyno Cytec), 42.9 g of a standard aluminum bronze,previously stirred to a paste in 56.2 g of butyl glycol and 31.6 g ofn-Butanol and a mixture of 19.8 g of a standard acrylate thickener(Latekoll® D from BASF) and 50 g of deionized water are processed into apaint. The pH value is adjusted to between 8.00 and 8.30 withdimethylethanolamine and deionized water is used to adjust the viscosityto 100 mpa•s (measured at 1,000 s⁻¹).

Application Example 4

The same procedure is following as in example 3. However, the 245.5 g ofmicrogel dispersion 3 is replaced by 234.8 g of microgel dispersion 5under the invention.

Comparison Example 1

The same procedure is followed as in example 3. However, the 245.5 g ofmicrogel dispersion 3 is replaced by 216 g of a microgel dispersionproduced from example 9 in DE 39 40 316.

Steam Jet Test:

Each of the aqueous basecoats produced in accordance with examples 3 and4 described previously and the comparison example 1 is applied with aspray gun on a 5×10 cm coated polycarbonate substrate in aclimate-controlled spray booth so that a dry coating thickness of 15-18μm is obtained. After intermediate drying of 10 minutes at 80° C., thepainted substrates receive a standard automobile industry 2K clearcoatfor plastics finishing with a dry coating thickness of 40-45 μm and thecoats are then baked for 45 minutes at 80° C. An X-shaped cross about 10cm in length with legs intersecting at about 30° is incised on thesecoated test specimens following Sikkens, using an Erichsen 463 scratchstylus with a 1-mm cutting tip.

The test specimen and the steam jet nozzle are anchored so that thecenter of the jet is located over the cross, the steam jet is parallelto one of the cuts, the distance of the steam jet nozzle is 10 cm fromthe test specimen, and the contact angle is 90°.

The test specimen is sprayed with water at 60° C. flowing at 11-11.5l/min in a trapezoidal jet pattern for 60 seconds.

The analysis is made by visual evaluation:

No chipping or creep up to a 1 mm maximum is O.K.

Creep of>1 mm up to chipping over large areas is not O.K.

The individual results can be read from the following table: TABLE IChipping after steam jet Paint samples Adhesion test Sample 1 Gt 0 1 mmSample 2 Gt 0 0 mm Sample 3 Gt 0 0 mm Sample 4 Gt 0 0 mm Comparativesample 1 Gt 3 9 mm

Table I shows clearly that, through the use of the microgel dispersionsunder the invention, finishes are obtained which excel due to goodadhesion to polycarbonate. The examples under the invention show furthervery good aluminum flake orientation and stability as well asoutstanding topcoat holdout.

1. Emulgator-free microgel dispersed in an aqueous phase, obtainable bya) producing a polyacrylate (A) in the presence of at least one compound(B) containing a phosphonic acid group, where the polyacrylate (A) hasat least one hydroxyl group and at least one carboxyl group; b) aqueousphase crosslinking of the reaction mixtule originating from step a) withan aminoplast resin (C); c) subsequent emulsion polymerization of thereaction mixture originating from step b) with at least one monomercomposition (D) which contains at least one radically polymerizabledouble bond.
 2. Emulgator-free microgel dispersed in an aqueous phase,obtainable by a) producing a polyacrylate (A) in the presence of atleast one compound (B) containing a phosphonic acid group, where thepolyacrylate (A) has at least one hydroxyl group and at least onecarboxyl group; b) aqueous phase crosslinking of the reaction mixtureoriginating from step a) with an aminoplast resin (C); characterized inthat the reaction mixture originating from step b) is not subjected toany subsequent emulsion polymerization.
 3. Microgel from claim 2,wherein the polyacrylate (A) originating from step a) is subjected toemulsion polymerization before step b) with at least one monomercompound (D) which contains at least one radically polymerizable doublebond.
 4. Microgel of claim 1, wherein the polyacrylate (A) is obtainableby polymerization of a monomer (i) with at least one polymerizabledouble bond and at least one hydroxyl group; of a monomer (ii) with atleast one polymerizable double bond and at least one carboxyl group; ofa monomer (iii) without a hydroxyl group and without a carboxyl groupwith at least one polymerizable double bond.
 5. Microgel of claim 1,wherein the compound (B) is an adduct from an alkyl-phosphonic acid witha compound containing an epoxide group.
 6. Emulgator-free microgeldispersed in an aqueous phase, obtainable by a) production of apolyacrylate (E) by copolymerization of a monomer (i) with at least onepolymerizable double bond and at least one hydroxyl group; of a monomer(ii) with at least one polymerizable double bond and at least onecarboxyl group; of a monomer (iv) with at least one polymerizable doublebond and with at least one phosphonic acid group b) aqueous phasecrosslinking of the reaction mixture originating from step a) with anaminoplast resin (C); c) subsequent emulsion polymerization of thereaction mixture originating from step b) with at least one monomercompound (D) which contains at least one radically polymerizable doublebond.
 7. Emulgator-free microgel dispersed in an aqueous phaseobtainable by a) producing a polyacrylate (E) by copolymerization of amonomer (i) with at least one polymerizable double bond and at least onehydroxyl group; of a monomer (ii) with at least one polymerizable doublebond and at least one carboxyl group; of a monomer (iv) with at leastone polymerizable double bond at and at least one phosphonic acid group;b) aqueous phase crosslinking of the reaction mixture originating fromstep a) with an aminoplast resin (C); wherein the reaction mixtureoriginating from step b) does not undergo subsequent emulsionpolymerization.
 8. Microgel from claim 7, wherein the polyacrylate (E)originating from step a) is subjected before step b) to emulsionpolymerization with at least one monomer compound (D) which contains atleast one radically polymerizable double bond.
 9. Microgel of claim 1,wherein copolymerization is carried out in the presence of an additionalmonomer (iii) without a hydroxyl group and without a carboxyl group,containing at least one polymerizable double bond.
 10. Microgel of claim4, wherein the monomer (i) is selected from the group ofhydroxyethyl(meth)acrylate, hydroxypropyl(meth)acrylate,hydroxybutyl(meth)acrylate and ε-caprolactame estered on ahydroxy(meth)acrylate base.
 11. Microgel of claim 4, wherein the monomer(ii) is selected from the group of acrylic acid and methylacrylic acid.12. Microgel of claim 4, wherein the monomer (iii) is selected from thegroup of hydroxyl group-free acryl(meth)acrylic acid esters and styrene.13. Microgel of claim 6, wherein the monomer (iv) is vinyl phosphonicacid.
 14. Microgel claim 1, wherein the aminoplast resin is a melamineresin.
 15. Microgel of claim 1, wherein at least one monomer compound(D) has at least one hydroxyl group.
 16. Microgel of claim 1, whereinemulsion polymerization is carried out in the presence of an additionalmonomer compound (D), which contains at least one radicallypolymerizable double bond and no hydroxyl groups.
 17. Microgel of claim1, wherein it has an acid number between 10 and 45 mg KOH/g.
 18. Amethod comprising preparing a multilayer coating, using anemulgator-free microgel of claim
 1. 19. A method in accordance withclaim 18, wherein the multilayer coating is a basecoat.
 20. A methodaccording to claim 18, wherein the microgel percentage, relative to thesolids of the coat obtainable therefrom, is between 20 and 85%.